Please help Urgent

What exactly is the problem or symptom? Exhaust whistle? Are you referring to a leak or is someone pulling your leg?

OHHH! :)

That has nothing to do with how the engine runs. Sure it might fall off the tail pipe but if anything were to plug the pipe, the engine would stall. Basically it's a giant air pump. It sucks in air, adds a little fuel, burns it to expand it, then pushes it out. Blocking that air flow anywhere will cause the engine to stall but nothing will be damaged.

Some people used to pull a prank by stuffing a potato into someone's tail pipe. The engine would start, then either stall or blow "splattered potatoes" all over the place. That's it.

Without knowing if there are any other related details, my guess is your friend had a running problem before and needs someone else to blame his troubles on. I can't imagine what a mechanic is going to find to solve the problem but I'd like to know when he does. A blocked exhaust can cause a temporary pressure buildup that can cause spitting back in the engine but nothing is going to get sucked into the tail pipe; it's going to get pushed out.

One real-world problem that can happen to any vehicle is a plugged catalytic converter. That can cause a severe loss of power if the engine will even run. It will also idle unusually smoothly and quietly, and it will spit back through the intake because of that excessive back-pressure. Still, once that plugged converter is replaced, the engine runs fine with no other damage.

Running problems are caused by engine sensors and other mechanical things in and on the engine. When the mechanic is done, lets figure out how that parts he replaces can be damaged by something in the tail pipe.