are after market axles heavier than stock? just wondering if the weight difference would make a noticable difference in the power?

 

An aftermarket axle will be lighter, improving the power.

 

Most aftermarket axles are heavier. This is simply because most people buy aftermarket axles that are wider than stock, and a little thicker for strenth. These are definitely heavier. They usually have a higher carbon content for added strength, but I don't think that necessarily is the reason they're heavier.

The one noteable exception is an axle specifically for drag racing. These are usually narrower than stock and also made out of aluminum. These are way lighter than stock.

The power difference due to the added weight is negligible. It is extra rotating mass which theoretically does cut into the power, but realistically, the small amount of added weight is so close to the center of the rotating assembly that you really can't tell the difference.