Mark IV got louder when press "Loop" button on footswitch

[Jazzdarkside]

my IV is A version
normally i play it on my bedroom with the output knob is about "1 - 1.5" when i press Loop on there is no any louder

but today i took it to recording studio so i can reach "2 - 3" on output knob and when i press Loop on it became very louder !

is this normal , or my IV got some problem ?

thanks

 

[Steve@Russo]

the volume boost might be something IN your effects loop, try a couple pedals out one at a time to find the suspect