Hi all, my bmw 320d e46 2004 sport mileage 109000 has recently developed a sort of chirp sound In the engine bay hot and cold constantly there started a few days ago and gradually got worse, can the e46 experts relate to this sound?, what can it be?, I am attaching a sound clip, any advice would be useful, thank you.

Voice_005.m4a

That’s A metallic sound. Does it change on revs?

firstly check oil levels on the engine. 
I would think the noise is a bearing from a pulley. Most likely the alternator or air con pump. 

The Belt Tensioners are another possible cause

Dave

The air con pulley has a kind of slip bearing on it which would make this noise if the air con is off. Turn the air con on and see if the noise stops when the clutch on the pump engages. 
it definitely sounds like something attached to the belts rather than the engine itself. 
I had an old e36 4pot which had the pulley with the knock sensor on it. That bearing failed and allowed the pulley to move forward and back. Try pulling each pulley away from the engine and if one moves, it is a good place to start 

I had a "chirp" sound on my 330Ci a while back which turned out to be the alternator.  New brushes fixed it & bearing...yes im tight!!!!!

Hi everyone thanks ever so much for the input. I had a mechanic look at it today briefly he claims it's coming from front exhaust side flexi?, anyone had any experience with that sort of issue?.

Hi everyone thanks ever so much for the input. I had a mechanic look at it today briefly he claims it's coming from front exhaust side flexi?, anyone had any experience with that sort of issue?. And no noise doesn't change with revs remains the same sort of a constant chirp

I missed to mention prior to the noise appearing. I removed the rear exhaust heatshield as it was loose and causing a racket. Moreover yesterday I held the back box firmly and noise almost went away!, could it need a new heatshield?.

Bizarre! 
sounds like it’s exhaust related then... make sure all the bolts are tight. Are the exhaust joints rubbing when the engine is running? Could it need exhaust paste? 
heatsheild could be rattling but it doesn’t make that noise, it would be much louder if it’s loose. As you held the back box and the noise stopped, I would look at exhaust mounts and all clams and joins of the system right through to the manifold. 

Certainly is bizarre!. Funny you mention the heatshield initially it was rattling and I couldn't take the sound like you mention it was loud, hence I removed it, it was in bad condition. I Haven't put a new one on. Thanks Im going to take it to a mechanic on thurday, hopefully it gets sorted. 

We all love a scary problem to turn out to be a cheap fix!!!!

Right guys, the loud metal to metal noise was the Exhaust it was loose!!, metal plate and welding done the job, got the rear discs and pads as it was an advisory last mot. Moreover the little knock from exhaust sides is still there, mechanic said your has had a new cat and it seems there's a stone or something in there that's making the noise?