1990 300CE, sloshing water sound

[jp*mc86]

Hi all, today I heard a weird noise coming from behind the dashboard of my 300CE. It sounded as if water was sloshing around behind the dashboard. There was no leakage inside the car, my heater core seems fine. I inspected under the hood, did not detect or find standing water. Later in the day the sound went away, now I'm more suspicious than ever. Does anyone know of a water collection point under the hood? There was no evidence of water leaking from beneath the car. Has anyone experienced a similar situation? Any ideas and help will be greatly appreciated. Yes it did rain the night before and my car has been through many down pours without incident.

Thanks