So my mini cooper s with 117k miles on it has pretty loud... what I think are the fuel injectors? I used to think this was normal but two people now have asked me what the noise is. I don't believe I've heard them this loud on any other car. Under moderate to heavy throttle applications I can hear them ticking away, and the speed they tick at goes up with the RPMS. It's very consistent, like a card in a bicycle wheel. I'm not sure if the sound has always been there, but the car drives normally otherwise and it's not loud enough to the point where it's overwhelming.

Not sure if it matters, but I have a 15% pulley reduction, so I guess the fuel injectors must be working a little harder than normal. Is this normal with these cars or is it something I have to be concerned about?

 

The injectors don't work any "harder" when the engine is under load. They just stay open for longer period of time to deliver more fuel. So, I doubt what you're hearing is the injectors.
Get a hold of a mechanic's stethoscope (or use a piece of hose as a makeshift) to isolate where the noise is coming from. It doesn't sound normal so you should definitely investigate it further.

 

What ^ said. A mechanic's stethoscope can be had cheaply at Harbor Freight. It's a great piece of equipment to have around. I can't imagine any scenario when you would be able to hear your injectors. I would lean toward lifter noise.

 

Alright, done. I think it's my timing chain tensioner. I used a stethoscope and put it on the timing chain cover, it sounds pretty chaotic. Is there anyway I can completely rule out the lifters? I'm going to replace the tensioner anyways since my car has 120k miles on it and I don't think the previous owner ever did it.

 

If you have an R50, R52 or R53 the bushings on either end of the black hydraulic rod (looks like a small hood lift) that is part of the belt tensioner sometimes dry, crack and fall out. That makes the hydraulic rod vibrate against the bolts at either end. It's easy to check by removing the passenger side wheel and fender liner. That's a cheap fix and worth researching before you spend too much money looking for a lifter issue.

 

I can't say I've ever heard fuel injectors from a MPFI engine make noise. Direct injection, on the other hand, is quite the racket.

Try running the engine with the serpentine belt off to eliminate the PTO as the source. That's another cheap and easy diagnostic step.

 

More than likely hydraulic lifter noise. Very common.