Crate Taxi 30e buzz crackle

[guitarhead]

Hello, i have a Crate Taxi 30E (battery powered) that buzzes on 3 chords - B, C, C# at lower volume (below 5 on the nob). It crackles when the volume is move to 5, dial goes to 10. It does not do it on other chords only on those 3 chords up and down the neck of the guitar -- i have used 3 different guitars and the amp does the same thing (Fender strat, Squier Strat, Fender Tele). What i hear is almost like a torn speaker cone and almost sounds like the whole amp vibrates to it. Also notice that the battery indicator light goes red when it's doing it even though the battery is fully charged or even when the amp is plugged into a wall socket. Manual says it should only turn red when the power is low. Everything else on the amp works fine. Anything i should look for when i open this thing up? Should i replace the 8 inch woofer, could it be the 2 inch piezzo tweeter? Is this a sign of a failing component in the amp? Any advice is much appreciated.

Thank you in advance.