Help - Car pop

HI,

Had my 1.4 tsi mapped and has a custom exhaust.

Pops and bangs now and then but noticed recently on motorway if doing 70+ and foot on accelerator the exhaust will pop and the car will jutter back and forth ever so slightly.

Is this normal?
Was thinking of doing a leeds-london trip this weekend - want to make sure its all good and i wont break down!

thanks,