Whenever I accelerate below about say 1200 or 1300 rpm or whenever the engine's stressed like when going up a hill I hear this scraping sound coming from the front of my truck. It's not throwing codes and it's fairly well maintained. Any ideas?

 

Loose belt? Bad bearing in alternator/power steering/idler pulley goraning under pressure?
Something loose in the suspension getting a wierd harmonic in that RPM range?