I concur with Gerald. Having worked as a consulting Mechanical Engineer, it's my experience that the lack of consideration for relief/fresh air to make-up the air you are exhausting, is the most often encountered problem with retrofit ventilation equipment. There is only so much static pressure that a fan can overcome (and residential-grade fans are not designed to overcome very much).
The big offenders for increasing your static pressure are
- excessive length of duct from fan to outlet
- fittings (90 degree elbows are the worst, use two 45 degree elbows if you can)
- no free-flowing fresh air source to provide make-up air
Also, dryer hose with it's accordian walls is not a good choice (it's static pressure per foot is much, much higher than rigid duct)...use rigid duct if you can.
Your choice of fan (in excess of 400cfm) is greater than 4-times the average household bathroom fan...so likely it's starved of air and thereby not running at it's advertised flow rate. Try cracking a window or two next time you use it and see if it works better.
With an oversized fan, it is not uncommon in a well sealed house with all windows closed, to create a backdraft down your chimney/flue and blow out your furnace and/or water heater's pilot light...so no relief air can create more than an odor problem!
Hope that helps,
Cheers