04 Bruin 350 auto - possible piston slap

I just bought a 04 Bruin that has a very strange knocking. Guy I bought it from said it sounded like his buddy's grizzly so he never thought anything of it. I have read that some with this problem say it needed a value adjustment. Both stealerships I stopped my said it sound like it was coming from the automatic belt housing area. The second fellow seems to think if the belt is not the problem them could be a piston slap. This was based on the blue smoke coming out of the exhaust when first started. Has anyone else had this knocking sound? What does a piston slap sound like and how bad is that? Will I be needing a new topend in the future? Thanks in advance for your advice.