I have recently had a new exhaust fitted to my 2.0 10v s70

its actually the third exhaust in 4 months

the garage say they have fitted it correctly yet it does not appear to have a resinator fitted when the original did.

This creates a large humming noise when driving and is particularly bad on a motorway (highway) louder than the radio

I am right in assuming the cheap exhaust I believe they have fitted is causing the problem is could it be something else

 

Sounds logical to me. What country are you in?

 

Go back and ask them to put the resonator back in. That is actually an important part of the exhaust system... the muffler only MUFFLES sound... the resonator actually is a tuned part that cancels certain annoying frequencies... frequencies that cause rattling and vibration. Their functions are complimentary, NOT redundant. Not adding a resonator is a way custom exhaust shops skimp to save money. Some cars don't have a whole lot of noticeable harmonics, and the resonator isn't as important. Other cars... like yours, apparently, DO have annoying harmonics, and the resonator is arguably more important than the muffler is.