(If not for the engine with the rumble....) With both engines apparently fluctuating, reduce one throttle and see if fluctuations on the other engine continue. If fluctuations continue, return throttle to full open and repeat process with the other throttle. One engine might have a problem and the other is normal but trying to compensate.
The rumble in ENG #1 needs to be fixed first, sounds like compressor damage or bleed valve issue causing that one.