I dont think the 555 problem is caused by grounding problems. Its on the same PCB using the same ground as everything else. The smoke machine itself is definately earthed correctly and ive had the same problem in a few different buildings. The PIC also resets if i plug something like a soldering iron or big transformer in and the ignition on our gas cooker causes a reset too. These things have affected every PIC circuit ive made so i guess they are normal but im just wondering if the 555 is creating a similar kind of interference thats so small that it only causes a problem when its connected to the same power rails as the PIC.