That's the exaust manifold heat shield. It's not a huge deal if it's rusty since all it does it reduce the radiant heat from the exhaust that hits the other parts nearby. You'd probably notice an issue if it came loose and started squeaking.

The exhaust manifold is the part that collects the exhaust from the four cylinders into one pipe. It gets really hot, so be careful touching it if the car had been on recently.

 

Thanks!
Along the lines of noises... could this cause a slight metal rattling noise? I've notice such first thing in the morning when I first start driving, maybe in the first 3km, when I turn a hard right. No other noise or vibrations though.

 

Your well used Subie simply wore out those sacrificial bolts from (science of metallurgy) as dissimilar metals (heated) accelerates galvanic reaction of one metal sacrificing itself over years. If stainless replacements were used, leave it as is. Shiny plated bolts work fine too. As you probably know, stainless hardware are very corrosion resistant in marine or river environments.

Rattling may be what you just repaired otherwise you might have to open the engine hood before starting up, startup and get out of the car and look/listen where the rattling is coming from. If not in the engine area, then it may be another exhaust shield under the car or towards the rear as heat shields are thin pressed sheet steel, galvanized for corrosion resistance but eventually corrode at their mounting points creating a larger hole than the bolt, beginning a rattle. Guess how I know this?

 

Thanks again Nutjob. They deffinitely are stainless, being meant for a sea kayak. However, I'll have to get the mechanic to tighten them better.... I had to make my arms into Gumbie's just to get those bolts started.... not very do-it-yourself friendly design!

 

Some of us resort to Gumby-like contortions when working as diyers. You're no different but save money by not paying someone to do it if saving on hourly labor rates.

 

Those could definitely rattle, but it's hard to be completely sure where a rattle is coming from. You can access it from below, but you'd have to remove the plastic engine splash shield first. That involves a couple dozen screws and plastic clips.