Peugeot 206 intermittant swishing watery noise behind dash

Clutch broke so took it to nearby Peugeot garage, whilst mending they said spension needed fixing otherwise wouldn't pass MOT. Went on holiday for a month straight after getting car back. As soon as drive it after holiday car was miss firing and swishing watery noise behind dash. Took it back to garage and they denied it had anything to do with them, said coolant leak was causing noise and miss firing. Did whole load of diagnostics couldn't find problem then said was head gasket. Took off and then said it needed skimming. Said they sorted but when went to pick it up car didn't start. They jet for a further two weeks to try and sort problem. Finally said sorted so collected car. But can still hear swishing watery noise so take it back. They say they can't hear it anymore and have cleared out sills and topped up gas in air con. Checked for leaking radiator by feeling carpets in foot wells. No joy. I am going mad with this noise and noone seems to have any solutions. Please help.