Bass leaves after amp warms up?


I don't understand-after my Musical Fidelity M6i amp warms up for about an hour I notice the deep bass & kick drum aren't the same.
They sound less musical with loss of weight/depth.The notes are there but the moving of air have left.Sound is has much less impact and boreing.
I had the same problem with Bryston amp so there is no defect with amps nor with the rest of my equipment/
PSB Synchrony one speakers,AQ cables,Bryston CD Player.
My question has anyone heard similar & is there a plausable reason?
fishing716
Also, just to be sure, I assume that when you disconnect and reconnect the speaker cables you have the amplifier turned off while doing so.

Yes of course Al
I have an ad running on Audiogon but don't see the buy it now or ask questions option on my end.
Is that something new or is there a mistake
Here is my ad under cd players:
Naim Audio CD5 XS
Can someone tell me if the ad is functioning correctly
Short of moving some of your equipment to another location, you might try monitoring the apartment voltage and seeing if there are any dips happening when sound goes bad. A hand held RFI detector is also a good investment.
I did move the equipment to different locations with no positive results.
There is no dips in my votage,confirmed by an electrician
"I'm more than beginning to suspect a curious "malfunction" in my processes if not hearing/interpertation."

Again, SPL meter would help establish if the effect is real/physical/measurable or not if in doubt. If it can be measured, then you know with confidence what you hear is for real and not an artifact of your hearing or how you listen.

IF nothing measures, then two options:

1) try an amp that is clearly better for the job
2) track down Mr. Freud and see if he is available. :^)