2007 A4 2.0tdi 140 multitronic , 87k .Had the car around a month and the intercooler has blown the seal out at the top , allowing air to escape under pressure . Fitten new intercooler today , but the damaged one taken out isn't an original part . What could cause the build up in pressure to cause this ? , there is also a slight slight whistle (siren noise) when turbo is active is this something to worry about ? Or normal ? Any advise would be appreciated!!