Question about 49 MHz Band

I think you are right. You should be fine. One thing to watch out for would be splatter if the sound card output is too high for the mic input. You will probably be able to hear that in audio distortion too.

More info about the 49 MHz is on this site here:

Part 15 Digest for Low-Power Transmitters

and says:

     d.  (15.235) 49.82-49.90 MHz

         (1) Field strength limits for non-homebuilt devices (or home-built devices constructed per Section 15.23 [Item 06 above] but not using alternate standards):

             (a) Desired signal not over 10,000 microvolts/meter at 3 meters

             (b) Extraneous emissions in-band and up to 10 kHz above and below band edges at least 26 dB below unmodulated carrier level or not over 100 microvolts/meter at 3 meters (whichever is stronger)

             (c) Any emission more than 10 kHz above or below band edges not over limits in Item 10 (Paragraph a)

         (2) Alternate standards for home-built devices made according to Section 15.23 (Item 06 above):

             (a) No more than 100 milliwatts total power input to transmitter (not just final RF amplifier)

             (b) RF carrier and all modulation products contained within band edges

             (c) Single-element antenna not over 1 meter long permanently attached to transmitter enclosure

             (d) Out-of-band emissions at least 20 dB below unmodulated carrier level

and Jon S. has info here, scroll down to 49 MHZ info:

http://home.att.net/~weatheradio/part15.htm

You should still be in compliance without any problems. You're not transmitting anything that wouldn't be if you put the transmitter next to your computer speaker and that would be allowed.