My 550sx has been running flawlessly all season. Earlier today, I noticed that it was making a strange sound (almost like a grinding noise?) at about 3/4 throttle and it wouldn't go any faster. At lower speeds, it seemed to run fine. Then later today, I checked all the wires/tubes to make sure nothing was loose and went to re-start it. The engine wont start and it makes this really loud metallic noise. It makes this noise whether the key is in or not. Any ideas? Did the engine somehow seize? With only a few weeks left to ride, I'd really appreciate any thoughts! Thanks in advance!