using PostgreSQL 9.1.2

I'm seeing excessive CPU usage and large amounts of writes to disk from postmaster tasks. This happens even while my application is doing almost nothing (10s of inserts per MINUTE). There are a reasonable number of connections open however.

I've been trying to determine what in my application is causing this. I'm pretty newb with postgresql, and haven't gotten anywhere so far. I've turned on some logging options in my config file, and looked at connections in the pg_stat_activity table, but they are all idle. Yet each connection consumes ~ 50% CPU, and is writing ~15M/s to disk (reading nothing).

I'm basically using the stock postgresql.conf with very little tweaks. I'd appreciate any advice or pointers on what I can do to track this down.

Here is a sample of what top/iotop is showing me:

Code:
Cpu(s): 18.9%us, 14.4%sy,  0.0%ni, 53.4%id, 11.8%wa,  0.0%hi,  1.5%si,  0.0%st
Mem:  32865916k total,  7263720k used, 25602196k free,   575608k buffers
Swap: 16777208k total,        0k used, 16777208k free,  4464212k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                                                          
17057 postgres  20   0  236m  33m  13m R 45.0  0.1  73:48.78 postmaster                                                                                                                       
17188 postgres  20   0  219m  15m  11m R 42.3  0.0  61:45.57 postmaster                                                                                                                       
17963 postgres  20   0  219m  16m  11m R 42.3  0.1  27:15.01 postmaster                                                                                                                       
17084 postgres  20   0  219m  15m  11m S 41.7  0.0  63:13.64 postmaster                                                                                                                       
17964 postgres  20   0  219m  17m  12m R 41.7  0.1  27:23.28 postmaster                                                                                                                       
18688 postgres  20   0  219m  15m  11m R 41.3  0.0  63:46.81 postmaster                                                                                                                       
17088 postgres  20   0  226m  24m  12m R 41.0  0.1  64:39.63 postmaster                                                                                                                       
24767 postgres  20   0  219m  17m  12m R 41.0  0.1  24:39.24 postmaster                                                                                                                       
18660 postgres  20   0  219m  14m 9.9m S 40.7  0.0  60:51.52 postmaster                                                                                                                       
18664 postgres  20   0  218m  15m  11m S 40.7  0.0  61:39.61 postmaster                                                                                                                       
17962 postgres  20   0  222m  19m  11m S 40.3  0.1  11:48.79 postmaster                                                                                                                       
18671 postgres  20   0  219m  14m   9m S 39.4  0.0  60:53.21 postmaster                                                                                                                       
26168 postgres  20   0  219m  15m  10m S 38.4  0.0  59:04.55 postmaster  


Total DISK READ: 0.00 B/s | Total DISK WRITE: 195.97 M/s
  TID  PRIO  USER     DISK READ  DISK WRITE  SWAPIN     IO>    COMMAND                                                                                                                        
17962 be/4 postgres    0.00 B/s   14.83 M/s  0.00 %  0.25 % postgres: aggw aggw [local] idle
17084 be/4 postgres    0.00 B/s   15.53 M/s  0.00 %  0.24 % postgres: aggw aggw [local] idle
17963 be/4 postgres    0.00 B/s   15.00 M/s  0.00 %  0.24 % postgres: aggw aggw [local] idle
17188 be/4 postgres    0.00 B/s   14.80 M/s  0.00 %  0.24 % postgres: aggw aggw [local] idle
17964 be/4 postgres    0.00 B/s   15.50 M/s  0.00 %  0.24 % postgres: aggw aggw [local] idle
18664 be/4 postgres    0.00 B/s   15.13 M/s  0.00 %  0.23 % postgres: aggw aggw [local] idle
17088 be/4 postgres    0.00 B/s   14.71 M/s  0.00 %  0.13 % postgres: aggw aggw [local] idle
18688 be/4 postgres    0.00 B/s   14.72 M/s  0.00 %  0.00 % postgres: aggw aggw [local] idle
24767 be/4 postgres    0.00 B/s   14.93 M/s  0.00 %  0.00 % postgres: aggw aggw [local] idle
18671 be/4 postgres    0.00 B/s   16.14 M/s  0.00 %  0.00 % postgres: aggw aggw [local] idle
17057 be/4 postgres    0.00 B/s   13.58 M/s  0.00 %  0.00 % postgres: aggw aggw [local] idle
26168 be/4 postgres    0.00 B/s   15.50 M/s  0.00 %  0.00 % postgres: aggw aggw [local] idle
18660 be/4 postgres    0.00 B/s   15.85 M/s  0.00 %  0.00 % postgres: aggw aggw [local] idle
Edit: A lot of the file writing seems to be to some temporary (?) files in the $PG_DATA/base/ directory. My understanding of the file structure here is that each table is basically stored as a file whose name is the OID of the table. However, there are tons of files named tnn_nnnnnnn, and it is these files that appear to be written to (perhaps written over) constantly. What are these files for? There is ~4700 of the files, and all are 8K in size:

Code:
-rw-------. 1 postgres postgres     8192 Jul  3 23:08 t12_1430975
-rw-------. 1 postgres postgres     8192 Jul  3 23:08 t16_1432736
-rw-------. 1 postgres postgres     8192 Jul  3 23:08 t28_1439066
-rw-------. 1 postgres postgres     8192 Jul  3 23:08 t24_1436243
-rw-------. 1 postgres postgres     8192 Jul  3 23:08 t24_1436210
-rw-------. 1 postgres postgres     8192 Jul  3 23:08 t19_1393372
-rw-------. 1 postgres postgres     8192 Jul  3 23:08 t28_1439051
-rw-------. 1 postgres postgres     8192 Jul  3 23:08 t8_1430334