UPt3 is a superconducting heavy fermion compound showing unconventional properties in the superconducting state. Ultrasonic measurements have played an important role in investigating these properties. Here, we present our longitudinal sound attenuation and velocity measurements in the normal state of UPt3 from 2 K to 300 K, for frequencies ranging from 85 MHz to 850 MHz, in a magnetic field up to 8 T. Attention was focused on the attenuation absorption peak developing at temperatures below 40 K, which was accompanied by a rapid increase in velocity. The center of this peak was located at about 10.5 K and within the experimental resolution, its position was frequency independent. The amplitude of this peak was found to be proportional to the square of the sound frequency. With an increasing applied magnetic field, the center of the peak was found to move to lower temperatures while the amplitude of the peak increased.