Backfire and an ugly noise

[Orono]

I have gained a LOT of knowledge through this site and now in need of more

I have a 05 Nomad 1600 with 45K miles.

Was out yesterday with a group and the better half for a cruise and all was good. Covered approx 150 mile no issues. we stopped to re-group and after 10 minutes I tried to restart. Turned over fine but would not catch. turned the key off/on (sometime the fuel pump does not kick in). Started this time but with a REALLY LOUD backfire and a bad noise...almost a squeek sound.

We were able to get home with out any decrease in power, the oil pressure did not change, temp was fine and no loss of power. Just that noise that changes with the rpm's.

I can confirm that it sounds like it is coming from the back cylinders

Some of the mods done before me are as follows:

Kuryakan Fuel Controller
K/N Filters with all the insides removed...reed valves, has backer plates, etc.
Cam Chain Extenders were done

Not sure where to start diagnosing this one, other than taking it to the dealer.

Thanks in advance for the feedback