Identify oil leak after oil change

Hello, need some help identifying an oil leak on Audi A4 '97 1.8 SE (non turbo) @ 125k

Since I changed the oil around 2 months ago the car has eaten around 1.5 litres of oil. I used the specific Audi Halfords own-brand oil (not sure if it's 0w30 or what?). I noticed the oil loss when I was stuck in traffic and revved the engine a little; it sounded like a diesel engine. Checked the oil and it was at min! Topped it up and after a while the same thing happened, sounded like a diesel. Checked the oil and It's back at the min level once more. Seems like it never goes past min, (or at least I notice it in time).

During the oil change I changed the oil filter but reused the sump plug. No oil leak is present around the oil filter or sump plug. They are bone dry clean. Before I changed the oil there was no oil loss from the engine (after 10k miles). There arn't any noticable leaks on the road when I park the car overnight.

Looking at my exhaust I can't smell any oil, but there is a little vapour (but I'm thinking I've a leak in the exhaust as there is a slight blow somewhere). There's no oil in the water and the water stays at the right level.

The engine looks the same as before from the top. I've crawled underneath and there is a slight drip coming from a piece of metal that sits towards the front of the engine (underneath the pullies) and in front on the sump. I'm quite sure it was there before I changed the oil but I can't be 100%. I can't see where this drip is coming from or if this is indeed big enough to cause the amount I'm losing.

A few days after I changed did the oil change I also noticed an additional noise coming from the engine when it's running; sort of like the noise an artists spray gun would make that is linked to engine speed. Again, I'm not sure if this is linked to the exhaust problem.

Any help would be appreciated.

Thanks