Why would you expect to hear vtec?
Its only the engine changing cam lobes, and there is not necessarily any different noise. I certainly don't hear anything much different until I get above 6000 rpm, and the vtec change was back at 4400 rpm.

If you really want to make sure, put a small indicator light across the vtec solenoid to show when the solenoid kicks in. You need a direct monitor on the working parts, and not your ears or butt-dyno.