Exhaust Manifolds

Earlier while on the road, I had some turbo and egr valve work done. All the while, my purpose in taking it in was to find a "Chirping/screeching sound" that became more pronounced when applying a load or decelerating with the exhaust brake. As the replacement of both of those items did not result in the reduction or elimination of the noise, the shop said it must be in one of the exhaust flanges of the manifold. "If we take it off, it will never go back on so be prepared to buy a new manifold". 1) does anyone have the same noise and was successful in finding and fixing same. 2) is it true that these exhaust manifolds warp so much that they can't be reinstalled even if removed when cold?? :confused013: Any input would be appreciated.