I have over 170,000 miles on my 2010 HHR and this morning on my drive I noticed the engine almost sounded like a four cylinder diesel, i did not notice this before.
Oil level is good, I checked after it cooled down and oil settled in pan.
Any ideas what caused this?

 

Sounds like you may need a new timing set.

 

I started it up again after it cooled down and it didn't sound that way, it sounded more normal. I am hoping it's nothing serious.

 

I drive about 19 miles one way to work over hills and a mountain of sorts.

 

If it is the timing set, it will become serious if you just wait and hope. It's a relatively simple matter to pull the valve cover and see if the timing chain is loose.

If there is some other cause, I'm sure someone else will say so, but with 170,000 miles, timing is very likely the issue.

 

X2 what RJ says! Sounds like a broken timing chain guide!

 

Would it act intermittently? I mean the engine was at operating temperature when I got to work and then when it cooled down it sounded better. Not trying to be contentious, just thinking out loud.

 

Heck, I have yet to figure out how to replace the engine air filter. LOL

 

Then it's not a job for you. It is near a 9 on the skill scale.

 

I have replaced my turn signal switch stalk, brake rotors and pads so I'm not totally ignorant of car repairs.