Engine ping under load

I Have noticed this for awhile. Just thought to bring it up to see if anyone else noticed it if you live in a hilly area. When accelerating up a steep grade the engine will ping(rattling metallic sound) when reaching a certain RPM, but stop pinging as i continue to push the accelerator down and increase the RPM. Should I be concerned? Could it be something else, loose exhaust heat shield or something? Or is this normal behavior for a gasoline engine? My old Honda Fit never had engine ping/knock that i can recall in its 200,000km of service running the same 87 octane gas.

 

Its got close to 71,000km. has been serviced on schedule by toyota dealership since new. I notice now if i hold it at a certain rpm going up a hill it will rattle continuously until i let off or push harder to change the RPM/load. I'll mention it at my 72,000km service see what they say. It could very well be a loose bolt or something. Its not really loud, never had a passenger notice it, only me as i've become attuned to every little noise my car makes.

 

I make a point of only filling up at "Top Tier" Gas stations. Usually Chevron; sometimes Shell or Esso. Then again, being I live at and daily drive near sea level and lots of hills(sea level to 950 feet above sea level on a daily basis), my ICE using 87 octane may be more sensitive to "bad gas". Perhaps I'll try your suggestion after my next service. I intend to start commuting to work by bicycle next week so i'll be using my car only for weekend trips. I'll keep this thread updated as to any changes in ICE performance.

 

I still notice it occasionally. It does seem to be temperature related. Hot days (above 20*c) I hear it consistently at specific rpm, low speed, climbing hills.
My next service is a ways off. Just filled up again at chevron(87 octane) on the weekend, my next fill up will likely be in a month or 2.

 

Just dropped her off for 72,000km oil change service. I mentioned the engine noise, they said it might be loose bolts on the exhaust. Will see what they say tomorrow. On a side note i was surprised they recommended to change the transmission fluid, which i agreed to have done. They told me the prius taxis have it changed every 80,000km.
They also convinced me to pay for the fuel additive(snake oil?) which is supposed to clean the injectors or something, maybe that will fix the engine noise?

 

hmm, well i never have received a recall notice for anything ever since 2 years owning my v. Maybe not enough owner complaints in Canada for them to issue a recall vs the much larger customer base in the US?
Regarding the engine noise, the service guy said nothing about the engine noise issue after the service, maybe he forgot to have them check it or he did and neglected to tell me. Regardless , i was tired when i picked up the car at the end of the day and didn't feel like pressing the issue. But, after 90 kilometers of aggressive highway/city driving today i never noticed any engine ping, maybe the snake oil injector cleaner really worked.