Mobo slot 1 = bad performance suddenly
 

When I plug my SATA HD into slot 1 of my PC's mobo (as opposed to slot 2), the following occur:

-boot time doubled
-choppy, unresponsive behavior during high-cpu usage
-flaky audio in/out
-lag during gaming significantly increased
-HD benchmarks awful (details and more below); other benchmarks fine

Also possibly related: The secondary hard drive stopped functioning properly last weekend (would hear series of faint noises like beep-click); eventually I would hear the platters stop spinning during operation. This hard drive is no longer plugged in. Selected data was lost; scandisk could not help.

Passmark performance test showed major differences in the hard drive's performance:
Scores for SATA slot 1 / slot 2:
--------------------------------
Disk - Sequential Read 3.3 / 46.4 (!)
Disk - Sequential Write 3.4 / 47.3 (!)
Disk - Random Seek + RW 1.8 / 2.9

Other diagnostics
-----------------
Memtest86 - 4 passes with no errors
Scandisk - no errors
Voltage readings - within range
Banging head on case - no results available

Pentium 4 CPU (2.4C with hyperthreading) Socket-478
Abit IS7-E with fail-safe settings
1 Gig Ram (4 X 256)
Antect 430 W Power
Windows XP Pro
Dual LCD Monitors
9700 Pro video

Any help would be appreciated!