Knocking or Heat Shield

Hello! Is it possible my Gen2 prius has very bad knock? or is it just more likely that a heat shield is rattling? Only possible thing I can think of is that the dealer just changed the coolant about 5,000 miles ago (currently at 140k). I don't have any OBD2 scanning devices to read coolant temps, but the fan rarely kicks on. It's winter here in Pennsylvania and doesn't get much warmer than 40*

 

To clarify, this only occurs under very high load (steep hills) and half throttle. Higher throttle makes it louder, it is a metallic rattling sound coming from the passenger side of the engine bay.

 

It has 140,000 miles of varied highway and city driving. I was thinking of using some redline. I used 87 octane (middle grade here in the States) and it's already running a bit better.

I'll take a look into that. I'm saving to get myself a torque wrench so I can install some new sparkies.

 

My previous car was a Mustang and I was paying 40USD per gas tank, now I'm paying 15USD with this Prius! I love it, and I can afford higher octane gas.

 

Running the 87 for a few days now and the sound has almost disappeared. I will run Seafoam intake spray and some Redline fuel additive and see how that helps me.

 

My bad, I am using 89.