My 2001 740i bmw makes a ticking noise when idleing and if i turn on the air conditioner it gets louder

could possibly be a lifter tapping (Ticking) ,depending on how many miles the vehicle has on it might be time for lifters to be adjusted,most foreign overhead cam engines must have lifters adjuster periodically ,if you turn on the air its puts more of a load on the engine causing a louder sound (also check oil level an engine low on oil will start to tick too.. the more wear the engine gets the looser the lifters can get over time ,look in your service manual if you have one and see what the intervals are on lifter adjustment this can give you an idea.
possible only if
the ticking sound is coming from the top of the engine usually comes from under the vavle covers where the lifters are located,

Hi, not sure from that end but how many km you have on that car, cose if it done 100,00.000-120,00.00 km You realy should pay attention or replace your timing belt, cos the noise you hearing could be from there not your valves, but if not changed in time the damage from that could escalate on that car to anywer $2-3 K, eazy. Anyway it just a thout 4 you. G/luck.
Tony

sometimes pieces from inside your catalitic converter break loose and make a ticking noise and would be hard to spot without the engine running

look at your idler pulley since the ac clutch runs on the serpintine belt its moving alot faster the berings are prob bad in it takes 10 minutes to take off and 17 dollars to replace n another ten but if you take it off spin it in your hand if its rubbing n stopping fast(should spen fast like a skateboard wheel) then its bad that could be all it good luck hope this helps

It could be but how easy was the belt tensioner ? that may be the problem by not putting enough tension on the belt. How tight is the belt ?

A ticking noise at idle I am going say your valves.There is someting going on with the lifter,The nuts that secure one of the rocker arm maybe loosen out, also make sure the sparkplugs are secured and are tightened up.

big end bearings( lower engine rod bearings to confuse) knock at idle and get louder with rpm
if the noise changes with rpm and you are hearing it near the ac compressor then it could be the ac pulley bearing
test if it is the compressor by listening and then turning the ac off the pulley will still spin but the compressor stops
if the noise remains , replace the pulley bearings

A lot of times a ticking sound is the valves, which usually means a valve job when it gets bad enough.

But if it is a gentler tick sound it could be what is know as a wrist pin knock, which in some cases is not a big deal and others a big deal.

If the sound gets louder and louder, you will have to do something about it. But if it stays pretty constant then you monitor it, and look for other indications such as losing power, excessise oil use, etc.

check your brake pads and rotors.make sure your pad arent completely worn out and scratching the surface of the rotors.

maybe is the air compresor and that's the noise that you hearing. Put the air in off if the noise stop, your problem is the compresor.