files appear corrupt, but aren't; kernel bug?

[Dan Christensen <jdc@jhu.edu>]

Over the past few hours, my potato machine has been behaving very
strangely.  Many of the files on my hard drive or which I read from
cdrom have minor errors.  Specifically, at a random point in the file,
two consecutive bytes are changed to 160 and 192 (240 300 octal).
Moreover, this often repeats every 4194305 bytes!  (That 2 to the 22nd
power, plus 1.)  Only large files seem to be affected, and this makes
sense given the large gap between the bad bytes.  However, I believe
that the files on the disks are fine because the problem goes away
sometimes.  For example, during a period when the computer was
misbehaving, I wrote a tar file to cd.  Now I get

% cmp -l copy-on-cdrom copy-on-hard-drive
2078721 240  53
2078722 300  74
6273026 240 127
6273027 300 374
10467331 240  46
10467332 300 304
14661636 240 344
14661637 300 151

Notice that the copy on the hard drive is now ok;  it was misbehaving
when the transfer was done, and so the transfer is corrupt.

Also,

% bzcap kernel-source-2.2.13.tar.bz2 > /dev/null

used to produce

  bzcat: Data integrity error when decompressing.

but now has gone back to being silent.  I ran bzip2recover on
the kernel source when it was misbehaving, and the components
differ from what the file now contains by 240 300 at one spot.

Can anyone tell me what might be happening here?  Is there
software I can use to help diagnose this?  

My hardware:  Transmonde Vivante SE, 6G IDE HD, scsi pcmcia card
hooked to Yamaha 4416S cdrw.

I read the list, but you are encouraged to cc your replies
directly to me.

Thanks very much,

Dan

-- 
Dan Christensen
jdc@math.jhu.edu