Have just got an intermittent deep sounding rattle or tap on the side of the engine

Any guesses what it might be Big ends, Timing chain, loose pulleys or what !!

It appears at idle or after I have blipped the throttle and the engine starts to slow back down to normal

Does it sound expensive ??

Thanks all

 

sounds like your chain and tensioners

 

Look also at your A/C compressor, perhaps you will see some kind of rust powder near the pulley.