When my fender rumble 25 combo amp is turned on and I then plug my bass or my son's guitar into the input jack, there is a LOUD pop. Then everything sounds fine as I/him plays. Likewise when we unplug the guitars and it is turned on. We get around this by only plugging in or unplugging when the amp is turned off.
If we turn the amp on after we plug in, there is no pop.
Does this happen for all combo amps, or is there something wrong with mine? Also, I'm pretty sure the electrical outlet is not grounded. Could that be why it pops?