要解决安卓WebRTC接收来电但无声音的问题，需要检查以下几个方面：

1. 确保权限设置正确：在AndroidManifest.xml文件中添加以下权限：

2. 检查音频设置：在接收来电之前，确保音频设置是正确的。可以使用AudioManager来设置音频模式和音频路由。以下是一个示例代码片段：

AudioManager audioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE);
audioManager.setMode(AudioManager.MODE_IN_COMMUNICATION);
audioManager.setSpeakerphoneOn(true);

3. 检查WebRTC初始化设置：在WebRTC初始化时，需要正确设置音频设置。以下是一个示例代码片段：

// 创建音频约束
MediaConstraints audioConstraints = new MediaConstraints();
audioConstraints.mandatory.add(new MediaConstraints.KeyValuePair("googEchoCancellation", "true"));
audioConstraints.mandatory.add(new MediaConstraints.KeyValuePair("googAutoGainControl", "true"));
audioConstraints.mandatory.add(new MediaConstraints.KeyValuePair("googNoiseSuppression", "true"));
audioConstraints.mandatory.add(new MediaConstraints.KeyValuePair("googHighpassFilter", "true"));

// 创建音频约束
MediaConstraints videoConstraints = new MediaConstraints();
videoConstraints.mandatory.add(new MediaConstraints.KeyValuePair("minWidth", "640"));
videoConstraints.mandatory.add(new MediaConstraints.KeyValuePair("minHeight", "480"));
videoConstraints.mandatory.add(new MediaConstraints.KeyValuePair("minFrameRate", "30"));

// 创建PeerConnectionFactory
PeerConnectionFactory.initializeAndroidGlobals(getApplicationContext(), true, true);
PeerConnectionFactory factory = new PeerConnectionFactory();

// 创建PeerConnection
MediaConstraints pcConstraints = new MediaConstraints();
PeerConnection pc = factory.createPeerConnection(pcConstraints, new PeerConnection.Observer() {
    // PeerConnection相关回调方法
});

// 创建并添加音频轨道
AudioSource audioSource = factory.createAudioSource(audioConstraints);
AudioTrack audioTrack = factory.createAudioTrack("audioTrack", audioSource);
pc.addTrack(audioTrack);

// 创建并添加视频轨道
VideoSource videoSource = factory.createVideoSource(videoConstraints);
VideoTrack videoTrack = factory.createVideoTrack("videoTrack", videoSource);
pc.addTrack(videoTrack);

通过检查上述方面，您应该能够解决安卓WebRTC接收来电但无声音的问题。