Hey Scotty

I drive a 2005 Volvo s40 T5 AWD that has just over 200,000 kilometres on it. I have an issue where water is getting into the rear right passenger footwell and front right passenger footwell as well. This only happens when it rains and only happens when it’s sitting outside parked for a while so I know it’s coming in from the top somehow. While I drive I can hear the water flowing back and forth as I brake and accelerate. I got it checked out by a mechanic and they said the sunroof drains are clear and they checked the trunk as well and found nothing. They told me they needed to remove the seats and the carpet to see where the rain water is coming from but I decided to decline because of how expensive that would be. What do you think is allowing the rainwater into the right side of the car under the carpets and what do you suggest I do? Thanks.