We've just had 35 m2 of good quality engineered flooring laid across lounge and study. It's about 20mm overall thickness with a 5mm oak veneer. The guys removed all the old skirting, glued the tongue and groove with PVA and laid it on existing floorboards with the recommended foam sheets between old floor and new. They used a series of ratchet straps to pull it together while the glue set. In places, when you walk on it, there is a loud cracking noise that is becoming very annoying indeed. Does anyone have any ideas as to what the cause of this may be please and maybe have a remedy?