92 Dodge Ram Van 350 Troubles with tires or something?Transmission? Lifters?

[Kel79]

Ok, here is the deal. I bought a 92 Dodge Ram 350 van. It is a 1 ton. It is extra long. I bought it to haul carpet in. The tires that came on it were 225/75/r16. They are 8 lug rims. These tires did not look right for the van considering we needed to haul heavy loads in the van. We ended up going with a little bigger tire, 245/75r16. We bought a set from a guy and the tires came off of a 95 Dodge Truck. The tires fit on just fine except when my husband drove it to the store, there was like this ping, ping, and it only did it when the tires were moving. Is there anything say mechanically that could be causing this noise? Maybe with my transmission???? Any help will be greatly appreciated!. Any help