Cold Air Return Filter

I was feeling energetic spring cleaning last weekend and removed the cold air grate from the wall and gave it a good scrubbing in the tub. Before I replaced it, I looked in and there were massive amounts of hair and dirt on that little "floor" behind the grate -- I guess that's the top of the furnace? I started removing handfuls of hairballs and tumbleweeds laying on top, and kept going until I got down to the metal. My house was built in 1956 and I've never removed the grate and took out all that hair before. We just had a cold snap the past two days and I turned the furnace on. I can hear the air freely going into that grate now (where I never could before), b/c all that hair and debris isn't buffering the airflow noise any longer. Started thinking -- was part of that hair and mess that I picked up also possibly a rotted filter laying on top? Like I said, everything I brought up was in black clumps so I'm wondering if there wasn't a dry rotted filter in there too? Did I do something wrong or is that space supposed to be free and clear? I hope I didn't just provide a direct route for hair and debris to go straight down to the furnace b/c there's nothing there to trap it now. Help please. Thanks.

replying to Lisa, Iggy wrote: A picture of exactly what you're talking about would've gone a long way. But, yeah it very possibly and even likely could've been the filter and it hadn't been changed in a decade or 2. Call in an HVAC guy or company to assess, clean and adjust the system for top performance and efficiency (it'll pay for the service call in just 1-year). As well as, explain if what you did was good or bad or has saved the life of your HVAC. They'll also write the exact filter size on the equipment (they ALL do and MUST have a filter), so you can have a stock of filters to change each year. I prefer the 3M Ultra Allergen filters, they've kept my entire HVAC like new for the past 10-years and tremendously reduced household dust or the need for dusting.