I don't know of any toilet that doesn't gurgle. Your husband sounds like a very meticulous guy :).

...note - not a toilet expert myself....

I only worry about noises made by the toilet or the toilet valve valve system when it's just sitting there (not flushing or re-filling). Unless he can see something like the valve leaking/spraying improperly when the tank cover is off during or after the flush, I'm thinking he may be looking for a problem that doesn't exist.

"My husband says he hears a gurgling in the toilet when it flushes. "

Most residential toilets use an S-trap that is designed to siphon to help clear the bowl.

The problem with S-traps (and why they are generally prohibited) is that they also tend to not make a good water seal after the siphoning action, and so trap priming is needed.

Tank toilets accomplish this by diverting some of the water used to fill the tank into the bowl during tank refill.
This then ensures that enough water is in the bowl to form a seal.

The 'glub' sound near the end of the bowl emptying is from the suction generated in the S-trap.

Air going into the bowl trap or out of the bowl trap when other items are draining often indicates a problem with the vent system.
The vents are present to limit accidental siphoning of traps as water moves through the drain lines.
Incorrect venting or a blocked vent can result in trapped air being forced out of the trap, or falling water creating enough of a vacuum to pull air in through the trap.