2001 jeep cherokee sport grinding noise when starting

My 2001 Jeep Cherokee sport 6-4.0LFI ( 4wheel drive) was rear ended. The tail pipe, rear leaf spring (I think), and right back bumper were damaged. The exhaust pipe was pushed forward and bent into the rear axle and was not drivable. The muffler, tailpipe and bumper were repaired and RT bumper mount bracket, RT end cap side bracket and shield were replaced. They also did 4 wheel alignment The next day there was a grinding clunk sound as it turned over to start. I have started it 3 times and the sound gets worse each time. The engine runs fine after its started. The engine was rebuilt about 6 months ago and has had no problems. Could this be damage from the exhaust pipe hitting something, or from the impact on the bumper?