My recirculating heater unit started making a bit too much noise for my comfort level, and I'm wondering what steps can be taken to quiet it down. I noticed that it quiets down with a raise the revs a bit with the gas pedal, but that's not really fixing it. The unit itself is firmly attached, as are the two metal flaps below. So.... where to begin?

 

In mine the foam around the core itself had given up so the core was rattling against the box, also where the pipes came thru the box. I put new foam in it, and a new core as the old one was showing signs of leaking, and put grommets around the holes where the pipes exit the box. Bottom line, take the box out and redo it all.......

 

right first undo the 2 + head screws under bottom dash rail behind lever and switch drop the heater down and check the top of heater for old coins pens as these things find their way there.....if no items found then remove the front which will be tricky their should be foam on the back of flap if none then replace.