2010 impreza wrx hatchback, can hear a ticking noise from the engine only inside the car at idle, comes from passenger side, almost like a diesel engine sound, can't hear it under the bonnet & it's been there since I've owned the car, anything to worry about?

 

Can you do a sound clip or vid?

 

Could be one of the fuel line dampers, next to passenger side strut tower in the engine bay. Had this tick/rattle at idle on my 2.5 Forester XT.

 

Could it beba relay or fuse failing?

 

I had exactly this on my 2007 Hawk STi about 4 years ago. Could only be heard inside the car...passenger side was where it was coming from.
I literally thought I was about to throw a rod or spin a bearing...it sounded awful, but only from inside, under the bonnet was nothing / completely normal.

My engine builder had a listen and said....that's a fuel line damper. I told him he must be kidding surely....he said....watch this.
He crimped off gently with pliers alternately each side of the two dampers. You could hear that the sound would disappear, then come back when he released the pliers.
Less than a minute to diagnose the fault and carry out the crimp test.

I couldn't believe how he knew in moments exactly what the issue was. I'm not sure if it was the fuel feed line damper or the return line damper....pretty sure it was the feed.
Whichever it was, I got the damper from Subaru with two bits of fuel line already attached to it, fitted it....job done.

The sounds travel down to the hard plastic fuel lines by the bulkhead and through the car....
I gently sliced along the last inch of the rubber line where it meets the bulkhead line, made it easier to get off and I was replacing that rubber line anyway of course.
I also recall using a hairdryer away from the car on the rubber end of the new fuel line to help soften it slightly and then pushed into the bulkhead end better / more easily.

Tools used :
Phillips screwdriver
2 rags
Pliers for wriggling off the rubber hoses
Razor blade
Hairdryer for 10 seconds
I kept a small fire extinguisher handy...just because.

If you end up doing this job, best to leave the car a few hours after running it - to fully cool down and for the fuel pressure to drop off. You do lose a tiny bit of fuel, but nothing a few cloths can't deal with.
And watch those VPower fumes....man they kick like a mule