56 reg C4GP sounds like an exhaust blow but exhaust is fine

Hi, I recently had a cam belt change on my 1.6 diesel. I picked the car up and it sounded like it had an exhaust blow and was lacking in acceleration. I took it straight back to the garage checked it over and couldn't find any blow. I took it to another garage they said the same.

I've checked the resonator and it's attached to the air filter housing. The acceleration is only when pulling away . It's almost as if the clutch is taking its time to engage.

Any ideas on these problems? Thanks