Nah, I don think its the heatshield.. Its a bit too deep of a sound.. I imagine heatshield would be more... i dunno.. You know when you're chain ballses up on your bike? lol! Its that kinda sound 
Also, quick question while Im here,
1998 prefacelift.. What are the sidelight bulbs I need? Im lookin at some LED W5W bulbs. Are they right?
