First step in cases like this is usually to unplug the card from the motherboard and re-seat it into its ISA slot. If the problem remains, try a different ISA slot just to be sure. If after all that, the card still has the same symptoms, you may want to look at other things which could degrade such as capacitors on the motherboard or within the power-supply, but before that you would want to go ahead and disconnect/reconnect the power cables from the PSU to the motherboard, just to check for a flaky connection.

Hey, if any of this fixes the problem then you may want to get a can of DEOXIT to clean/treat all your connections, including the ISA slot and SB32 you're using.

Logistics wrote:

First step in cases like this is usually to unplug the card from the motherboard and re-seat it into its ISA slot.

Tried it, but the problem is still remains. Plugging card in different ISA slots is almost impossible due of VRM components on my mainboard and card length.

UPD: in DOS now all OK (even 8\16 bit playback thru DSP!) with old mixer settings (max master volume), so it is more a Windows problem, but I will try to clean ISA slot and connectors on my card. I will check my PSU also (mobo caps are fine, no leaked or exploding)

UPD2: Just tried on fresh installed Windows - still freaks up the sound. I also tried to clear CMOS and try again - no luck.
BTW, the chipset on my mobo is VIA Apollo VPX

Two things I can think of:
1. The Win98 stock drivers SUCK - I get distortion with almost all my creative cards in win98 until I install the latest drivers from creative - then the problem goes away.
2. I got the same distortion you are describing with my Yamaha YMF719-s. Turns out, the card has an amplifier circuit for headphones witch can be disabled. Moving two jumpers on the board solved this. Similarly, my SB PRO 2 has one SPK output and one Headphone output - the latter being amplified and causing distortions on speakers. Moving the jack from one output to another solved the problem.

kanecvr wrote:

The Win98 stock drivers SUCK

Reinstalled soundcard drivers - still distorts, BUT if I connect to speaker (= amplified) out, it sounds a lot louder but more crisp! 🤣 I think that DC decoupling caps on card' line out are just leaked (i.e. I noted a different DC offset levels on left\right channels, while if unconnected they stay on 0V level).

Quite possible - found the same problem on a CT4500. Left channel was clicking and buzzing regardless of volume. Removed most of the caps, measured them with a capacitance meter and found a couple of them were way out of spec.