Strange thing happens when I bias my amp

I tried to bias (at 100 mA) my newly acquired used Cary SLI-80 integrated using a standard multimeter set to DC current. WIth no input signal the bias current was over 200 mA initially, then decreased (seemingly) exponentially to 0 with a time constant of 1 to 2 minutes. This happened in both channels. The amp works well and sounds great to me by the way. I am curious as to what's going on and would like to know if there is a problem I need to address. Any advice from members with expertise in electronics is appreciated. Thanks in advance. Dave
For ss amps, TNT Audio has a great article explaining how to set the bias of your amp. Google 'adjusting the bias of your amp'. But it doesn't talk about mosfets, only bi-polars. Mosfets are adjusted by removing a rail fuse and putting an ammeter (setting your multimeter to mA) across the contacts. One channel at a time. The fuse contacts, that is. Not the mosfets. Ideally both channels at the same time with separate multi-meters.
Basic guesses are usually the best guesses and that is:

your multimeter settings are wrong

you are grounding improperly

some connection sequence is incorrect

Regardless, contact Cary for further instructions.
I have an SLI-80 F1 and have never had any issues biasing a variety of tube types. I haven't seen the behavior you're describing.

I would agree with Celtic's recommendation to look first at the multimeter itself and test with a different meter. You can get a Craftsman meter from Sears for around twenty dollars that should work well enough to see if the issue is with the amp or the meter. There's a Fluke available on ebay for $28 that might be better than the Craftsman.

Advice from Cary's service department has always been good but for an issue like what you're describing I'd be willing to bet they'll want you to ship the amp to them. That's an expensive and potentially risky proposition because of the risk of shipping damage. As you know, Cary's packaging is very good but that's a very heavy amp.

What kind of tubes are you biasing at 100 mA? The manual says 75 mA without mentioning the tube type and the advice I got from Steve at Cary suggested 65-70 mA for El34 and 6L6 tubes.