Had an experience on a 767 once where an unpleasant smell wafted through the aircraft at TOD. No biggy. Mentioned it to the the engineers after landing. Ground test OK (ha ha). Next sector same thing. Futher investigation revealed nothing. Next sector had a staggered descent and the same smell went thru the aircraft each time the throttles moved to idle thrust. This time some pax and cabin crew felt a bit off. At the aerobridge both pilots and most cabin crew have watery eyes and a headache. Aircraft grounded. Group think-NO. Continued exposure-YES.
Wash up. Problem caused by a faulty bearing in a ground air cart in Sydney (plane dispatched with APU inop) which had deposited a contaminant (hydraulic fluid) in the duct system exacerbated when high pressure bleed valve opened. Aircraft required complete clean of duct system. These things happen.