2002 Chevy S-10 Constant engine 'tap' and whining at accele

I just acquired a 2002 Extended-cab Chevy S10 with 89900 miles; 4 cyl engine w/ auto transmission. The previous owner was told that the problem was nothing to worry about, but I just want to get some ideas as to what it could be, etc. There is a constant noise, I would describe as a light 'tapping.' It isn't very loud, but is definetely noticeable. Upon acceleration, there is an additonal whining sound; I don't know how to describe it except that it sounds like the pitch of an electric motor. There doesn't appear to be any performance issues; it's just quite annoying (and a bit embarrassing). When I open the hood, the noise does appear to be coming from the motor, not the belts or anything else I'd expect to make a whining-type noise. Thanks, in advance, for any assistance!