Thanks gents. Yes, I tried whacking the top when playing and nothing happened. I tried wiggling the guitar chords, wiggled input jack but it seems to be solid (I will do a continuity check). While doing all of that I played the bass and no problem.
But what I did discover was this: every time after I re-started amp the siren sound would start after anywhere from 10-14 seconds then stop and everything would be fine. The siren sound would start and build quite rapidly then abruptly stop--this sound lasts approx.4 seconds every time. Then, the amp sounds fine and I play away no problem.
I repeated this on/off process five times and got the same results: 10-14 seconds all good, nasty siren sound for four seconds, then all is fine.
Note: the above occurs without the bass plugged into amp.
Cap discharging/charging?
But what I did discover was this: every time after I re-started amp the siren sound would start after anywhere from 10-14 seconds then stop and everything would be fine. The siren sound would start and build quite rapidly then abruptly stop--this sound lasts approx.4 seconds every time. Then, the amp sounds fine and I play away no problem.
I repeated this on/off process five times and got the same results: 10-14 seconds all good, nasty siren sound for four seconds, then all is fine.
Note: the above occurs without the bass plugged into amp.
Cap discharging/charging?