I cannot believe more of the communications guys on the board have not jumped into this topic.
There are a thousand things that can get ignition noise down to a minimum and some of them actually work. There are two paths: shielding or suppression. Shielding the interference by moving the antenna as already suggested or by bonding the hood to the body of the car with ground straps. This increases the shielding ability of the hood. Make sure the coax on the antenna has not rotted somewhere causing the shield to be broken. Replace it if it is old just because. Another trick is to bond the exhaust pipe in several places to the chassis because it will radiate noise the length of the car. The bonding I have used is the outside braid from communications coax such as 8298, RG 8 or any of the fat braid shielded cables. Amateur radio stores (NOT Radio Shack) have ground straps in stock that will work. They are not cheap.
A lot of the suppression suggestions are good ones. In my experience, resistive systems work best with the resistance distributed through the entire system: coil wire, spark plug wires, plugs.
Capacitors on the coil also help. Both on the positive and one on the negative ends.
If you have an old hand held AM transistor radio, try using it next to your engine and next to someone else's. If the noise is equal, then your antenna is probably bad. If yours is noisy, check for arcing. Look under the hood in the dark while the engine is running and look for sparking or corona.
I know the list is long but the problem is a pain in the rear (Yeah I know it is a family board).
Craig