My wife has a 2011 c30 t5 with roughly 170k miles on it (yeah she drives a lot)

Recently (month or two maybe) her car has started making an audible ticking sound at startup. The sound lasts for roughly 10 seconds or so then goes away and sounds normal.

In the past week or so we have started to get a smell of exhaust during that first startup period. Its quick and goes away just like the ticking sound.

We have heard one of two things with regard to the ticking, either sticky lifters or exhaust leak. Just before the sound started she switched oil from Pennzoil platinum to Castrol syntec high mileage, we have read that high mileage oil isn't great for these engines and will be switching back with the next change.

The smell makes me think exhaust leak of course, and we have read that some of the exhaust manifold nuts or turbo downpipe bolts can come loose. We tried to get a look at them today and of the ones we saw, nothing looked to be missing or have gaps. How do you tighten these if they are loose?

Any advice??